ISTP NEWSLETTER Vol 5, No. 2. Nov, 1995
http://www-istp.gsfc.nasa.gov/istp/newsletter.html
John Lyon's model, showing what happens when the shock impinges on the
earth's magnetosphere.
Article page 8
IN THIS ISSUE
Title Author
Periods of Upstream Field-Aligned (>10KeV) Ions in the Earth Foreshock Region - D. Berdichevsky
Satellite Hazards Revealed - Merry Maisel
The First Solar-Terrestrial Research Campaign of IACG - Michael Teague
A New Statistical Model of High-Latitude Convection - Mike Ruohoniemi
WIND/GEOTAIL Correlative Studies - Michael Teague
Key Parameter Availability - Mario Acuna
KPGS Programming for ALPHA Platforms - Gerry Blackwell
Polar Orbit and Attitude Issues - William Mish
Editor:
Michael Cassidy
CASSIDY@ISTP1.GSFC.NASA.GOV
Contributing Editors:
Steven Curtis - Science Editor
U5SAC@LEPVAX.GSFC.NASA.GOV
Ken Lehtonen - Data Distribution Facility
KEN.LEHTONEN@CCMAIL.GSFC.NASA.GOV
Kevin Mangum - Central Data Handling Facility
MANGUM@ISTP1.GSFC.NASA.GOV
Dr. Mauricio Peredo - Science Planning and Operations Facility
PEREDO@ISTP1.GSFC.NASA.GOV
Dick Schneider - ISTP Project Office
DICK.SCHNEIDER@CCMAIL.GSFC.NASA.GOV
Jim Willett - NASA Headquarters
WILLETT@USRA.EDU
Periods of Upstream Field-Aligned (>10KeV) Ions in the Earth Foreshock Region
D. Berdichevsky, S. Boardsen
D. Williams, R.W. McEntire
M Peredo, S. Kokubun
Upstreaming ions from the Terrestrial bow shock populate the foreshock region and contribute to its structure (e.g. S.A. Fuselier, E.W. Greenstadt et al). The custom Key Parameter plots produced at the ISTP Science and Planning Operation Facility (SPOF), see Figure (next page), helped to identify this preliminary selection of periods corresponding to observation of high energy (>10KeV) field-aligned beams.
The example presented here, from May 8, 1995, illustrates this correlation for a particularly simple geometry. During the interval in question, GEOTAIL was near the Earth-Sun line, at 21< Xgse<26, -6< Ygse<5, and -3< Zgse<-1 (see figure). In this case the sudden bursts in the bottom panel of the enclosed figure represent the observation of up-stream accelerated protons in the EPIC KPs, matching the simple geometrical condition of B approximate aligned with the X-axis (deduced from the MGF measurements) as seen in the upper panels of the figure.
These tentative events are proposed for further study by experiments on GEOTAIL and WIND.
References:
Fuselier, S.A., Ion Distributions in the Earth's Foreshock Upstream from the Bowshock, Adv. Space Res., 15, pp (8/9)43-(8/9)52, 1995, A Journal of COSPAR, a scientific committee of the ICSU.
Greenstadt, E.W., G. Le, R.J. Strangeway, ULF Waves in the Foreshock, ibid., pp. (8/9)71-(8/9)84
D. Berdichevsky,
berdi@istp1.gsfc.nasa.gov
S. Boardsen,
boardsen@istp1.gsfc.nasa.gov
M Peredo,
peredo@istp1.gsfc.nasa.gov
Raytheon STX Corporation ISTP/SPOF
Goddard Space Flight Center
Greenbelt, Md. 20771
D. Williams
R.W. McEntire
JHU/Applied Physics Laboratory
Johns Hopkins Road
Laurel, Md. 20934
S. Kokubun
Nagoya University
Terrestrial Environmental Laboratory
Japan
Satellite Hazards Revealed
Merry Maisel
Neither the U.S. nor any other country presently runs a "space weather prediction service." But new discoveries by a group of space physicists at Dartmouth suggest it may one day be a good idea.
"What we've found," says group leader Mary Hudson, professor of physics at Dartmouth (currently on sabbatical at the University of California, Berkeley), "is some very long-lasting effects of a well-known kind of solar activity called Coronal Mass Ejections (CMEs). In particular, we have found that very strong CMEs can induce the formation of new belts of energetic particles around the Earth, similar to the Van Allen belts, and these can last for months."
Hudson's group has been working in close collaboration with another group at Dartmouth led by John Lyon, a research professor who conducts large-scale, three-dimensional magnetohydrodynamic (MHD) simulations of the interactions of the solar wind with the earth's magnetosphere. Lyon has been using the resources of the Pittsburgh Supercomputer Center for these simulations, and graphical display capability provided by the Advanced Visualization Laboratory at the University of Maryland, in collaboration with Chuck Goodrich. "We take the results of John's simulations," Hudson says, "and we use the Cray C90 at SDSC to run a code that models the behavior of particles, electrons and protons in the same large volume of space."
Hudson's collaborators include research associate Victor Marchenko and graduate students at Dartmouth. "I am also working with my Berkeley colleagues Ilan Roth and Michael Temerin on this project, Xinlin Li and John Wygant at the Universities of Colorado and Minnesota, and Air Force affiliated experimenters with energetic particle data from the CRRES (Combined Release and Radiation Effects Satellite)," Hudson says.
Ejections of mass from the solar corona into the solar wind (the stream of particles from the sun that impinges on and shapes the Earth's magnetosphere) are very frequent occurrences, and scientists believe they are often connected with intense solar flare and solar prominence activity much lower in the solar atmosphere. Hudson's group is modeling an unusually strong CME that occurred in March 1991, at the height of the sun's 11-year "sunspot" cycle (the numbers of sunspots are the traditional measure of solar activity in general).
"This mass ejection caused a shock wave in the solar wind which traveled to the earth's magnetosphere," Hudson says. The magnetosphere on the day side of the earth normally protects the earth from solar wind effects out to about ten Earth radii. "Our models show that this particular CME compressed the dayside magnetosphere inside the orbit of geosynchronous spacecraft (6.6 Earth radii)," Hudson notes, "so it was a particularly impressive event, although not terribly unusual for solar maximum."
"Our modeling at SDSC (San Diego Supercomputer Center), suggests that the interaction of this shock with the magnetosphere set up long-lasting belts of energetic particles in this region of space which includes the region in which numerous satellites are located," Hudson says. The model results are in very good agreement with measurements of energetic particles made by the CRRES satellite then monitoring the region. "If this is borne out by future observations and modeling in the NASA Global Geospace component of ISTP (International Solar- Terrestrial Program), with recent launch of the WIND satellite to study the solar wind impinging on the magnetosphere, and upcoming launch of the POLAR satellite on January 12, 1996 which will pass through the radiation belts," Hudson says, "valuable information about a region of space previously thought to be relatively well insulated from solar shocks by the earth's magnetosphere may be obtained. Persistent belts of energetic particles can pose a threat to delicate instruments on a variety of communications, navigation and weather satellites, for example."
Her model includes more than half a million particles. Under the influence of the CME, particles "surf" inward on the solar shock, gaining energy. "A 1 MeV particle at 10 Earth radii can become a 25-40 MeV particle at 2.5 Earth radii," Hudson reports, at which energies such particles can penetrate satellite instruments. "We think that such energetic particles were detected during the CME," Hudson says, "and, more importantly, they persisted for months afterward."
The first two illustrations here are from John Lyon's model, showing what happens when the shock impinges on the earth's magnetosphere. (Lyon will be demonstrating this model in real time at Supercomputing 95 in December.) The third illustration shows the long-lasting particle belts that were modeled by Hudson.
"It seems that the well-known Van Allen belts are often joined by companions like these, particularly at solar maximum," Hudson says, "and it may be a good idea for those planning to launch or service satellites to be prepared for such events to recur at the time of the next solar maximum, about 2001."
Refs: Li et al., GRL, 20, 2423, 1993.
Hudson et al., GRL, 22, 291, 1995.
The above article will appear in the San Diego Supercomputer Center Newsletter, "Gather/Scatter", written by staff writer Merry Maisel. Color figures cited appear on the Dartmouth Space Physics web page, http://caligari.dartmouth.edu/~orient/space/title.html under the Theory/Mary Hudson-ISTP heading, Figures 2 and 3.
Merry Maisel
San Diego Supercomputer Center, UCSD-0505
University of California, San Diego
La Jolla, CA 92093
maisel@sdsc.edu
Mary Hudson
Physics and Astronomy Department
Dartmouth College
Hanover, NH 03755
maryk@sunspot.ssl.berkeley.edu
The First Solar-Terrestrial Research Campaign of IACG
Michael Teague and Jim Green
The following brief article will appear in longer form in EOS under the authorship of J.Green, A.Nishida, and L. Zelenyi.
At the present time the IACG has defined four campaigns:
- 1st: Magnetotail Energy Flow and Non-Linear Dynamics. Lead Coordinator: J.Green.
- 2nd: Boundaries in Collisionless Plasmas. Lead Coordinator: G.Paschmann.
- 3rd: Solar Events and their Manifestations in Interplanetary Space and in Geospace. Lead Coordinators: R.Harrison and D.Baker.
- 4th: Solar Sources of Heliospheric Structure Observed out of the Ecliptic. Lead Coordinators: A.Galvin and H.Hudson.
The 1st campaign is sub-divided into two phases: 1.The Structure of the Global Magnetotail System, especially during quiet periods, and; 2. Magnetotail effects of the Global Solar Wind -Magnetosphere interaction, especially during active periods. This article deals only with the first phase of the 1st campaign for which the broad objective is to gain an understanding of the large -scale configuration of the magnetotail system using the widely-spaced IACG spacecraft together with ground-based data, other spacecraft data and modeling tools. The specific questions to be addressed in the first campaign phase are:
- Boundary Region Structures:
- How does the thickness of the LLBL and the HLBL vary with upstream SW conditions (e.g., IMF orientation and strength)?
- How does the fine structure of the LLBL vary with upstream SWE conditions; do SW in homogenities penetrate into the boundary layer?
- What is the evidence for reconnection along the flanks of the magnetopause; how does the process vary as a function of upstream conditions (IMF orientation, plasma beta, Mach Number)?
- Where is the magnetopause locally open and closed; how does openness vary with upstream field orientation, distance down the tail, and time?
- How do the large-scale vortices in the tail vary with SW speed and IMF strength and orientation; what is the evidence that they are driven by a Kelvin-Helmholtz instability?
- Does the plasma sheet bifurcate, or form fingers, when the IMF turns Northward?
- How much of the SW electron heat flux enters into the tail lobes; how is this entry regulated by the IMF?
- Quiescent Configurations:
- Does the magnetosphere have a ground state during quiet conditions?
- What is the structure of the quiet-time magnetosphere?
- What are the sources of the magnetotail plasma?
- How does the high-latitude ionosphere respond to magnetospheric activity in quiet conditions?
- How do MHN waves transfer energy under quiet conditions?
- Origin of Plasma in the Plasma Sheet:
- What are the relative source strengths of the SW and the ionosphere?
- What are the underlying plasma-physics mechanisms, including convection, heating, and acceleration, that are responsible for the transport of plasma from these source regions into the plasma sheet?
The IACG core missions involved in the 1st campaign are the Geotail (ISAS), Wind (NASA), Interball-Tail (IKI), Interball-Auroral (IKI), and Polar (NASA) spacecraft. At the present time only the first three of these are on orbit. However, it is clear that many of the scientific objectives defined above can be met using these spacecraft in conjunction with, for example, the IMP-8, GOES 6 and 7, and the Los Alamos National Laboratory equatorial spacecraft and a variety of ground-based radar and other instruments.
Consequently, at the IACG Working Group 1 meeting in Sapporo, Japan on September 6, 1995, a number of time intervals were selected in 1995 and 1996 for the first phase of the 1st campaign.
They are as follows:
October 18-21; October 26-27; October 31-November 1; November 11-12; November 17; November 27-30; December 3-4; December 7; December 15; December 18-20, and; January 12. These intervals are all based on having a solar wind monitor (Wind or IMP-8) with Geotail and Interball-Tail near their apogees in the mid-tail regions.
To facilitate the implementation of the 1st campaign, a Coordination Committee consisting of A.Nishida(ISAS), M.Acuna (NASA), R.Schmidt (ESA), L.Zelenyi (IKI) and J.Green (NASA) as Lead Coordinator has been formed.
A major mechanism for disseminating information about the IACG campaigns is the WWW. The URL is http://iacg.org. The pages for the 1st campaign are presently undergoing reconstruction and expansion, however the present content includes:
- Campaign Science Objectives and Rules of the Road
- Descriptions of the primary IACG missions and the instruments involved in the campaign
- Contact information on coordinators and participants
- Summary of ground observation sites
- Spacecraft Trajectory plots for each time interval above
- Spacecraft groundtracks on a world map together with a variety of ground obsevation sites for each time interval
- Key Parameter and high-time resolution data plots (future use)
- An interactive plotting capability for Key Parameter and high-time resolution data (future use)
Any suggested modifications and/or additions to these WWW pages should be sent to J. Green at green@nssdca.gsfc.nasa.gov.
Michael Teague and Jim Green
Goddard Space Flight Center
Code 630
Greenbelt, Md. 20771
teague@nssdca.gsfc.nasa.gov
green@nssdca.gsfc.nasa.gov
A New Statistical Model of High-Latitude Convection
Mike Ruohoniemi, Ray Greenwald
We announce the availability of a new high-latitude convection model of general interest to the ISTP community. It is based on data collected with the Goose Bay HF radar over the period 1987 -1993. The model is suitable for any application that requires estimation of the large-scale convection and provides a point of comparison with the satellite-based models that have recently been developed.
The accompanying figure shows plots of the electric potentials in MLT/invariant latitude coordinates for the two signs of the IMF By component under conditions of |By| > |Bz| and Kp = 2+/3-. (The potentials at latitudes beyond the range of the measurements, 65 deg-85 deg, were solved by applying Laplace's condition with zero potential at 60 deg.) The two-cell pattern is strongly modulated by the sign of By. In particular, the dusk/dawn cell is more elongated in MLT for By-/By+. The difference in the potential variations associated with the two cells is larger for By+.
The model is expressed as an expansion in spherical harmonics. Depending on the application, the model output can be parameterized by IMF, Kp, and day-of -year (season). Tables of coefficients can be obtained from the authors.
Mike Ruohoniemi
Ray Greenwald
JHU/Applied Physics Laboratory
Johns Hopkins Road
Laurel, MD 20723-6099
mike_ruohoniemi@jhuapl.edu
ray_greenwald@jhuapl.edu
WIND/GEOTAIL CORRELATIVE STUDIES
M. Teague and J. Green
The 1st Wind/Geotail Correlative Studies Workshop was held in Hawaii, May 16-18, 1994. During this workshop three working groups were established to study Wind, Geotail and related data in the following areas: Magnetotail and Substorm Physics; Bow Shock, Magnetosheath/ Foreshock and Interplanetary Physics, and; Magnetopause and Magnetosphere. Two of these working groups established specific study intervals. NASA/GSFC Code 630 has established a series of WWW pages to provide both information concerning the spacecraft positions and instruments and the data acquired during the intervals. The URL is http://bolero.gsfc.nasa.gov/~solart/overview.html.
The positions of Wind, Geotail and IMP-8 during the 1st time interval for the Magnetopause Skimming Campaign
The majority of the information presently contained on the WWW pertains to three time intervals selected in the Magnetopause /Magnetosphere area during which the Geotail spacecraft was skimming the magnetopause while Wind and/or IMP-8 were monitoring the Solar Wind. The time intervals for what is known as the Magnetopause Skimming Campaign are:
- Day 351 (December 17, 1994), 0730h to 1700h UT. During this time period Geotail was skimming themagnetopause at 3h MLT, IMP-8 and Wind were located in the Solar Wind at 13h MLT and 8h MLT respectively, and the IMF was predominantly Southward with one dip to approximately 0 nT in Bz at about 1130h UT. An example of the spacecraft positional plots available on the WWW is shown below for this time interval.
- Day 352 (December 18, 1994) 2000h UT to Day 352 (December 19, 1994) 0300h UT. During this time the Wind magnetic field data start at 0 nT and builds strongly Northward, and Geotail is in the dusk flank.
- Day 361 (December 27, 1994) 1230h UT to Day 362 (December 28, 1994) 0100h UT. In this time interval there is a Northward IMF for approximately the first six hours of the interval followed by a Southward IMF for the remainder of the time period. Geotail moves from the dawn flank (passing in and out of the boundary) to the dusk flank.
Through local and remote access to other datasets at GSFC and in Japan, the WWW pages contain a substantial and growing volume of information and data concerning these periods including:
- Campaign summaries, Rules of the Road (in preparation), and usage statistics for the WWW pages;
- Summary of ground observation sites (under construction)
- Trajectory plots, instrument descriptions and contact information for campaign participants;
- Separate daily Key Parameter plots for Wind, Geotail, IMP-8 and Geosynchronous and Ground-Based data;
- An interactive plotting capability (at the prototype stage) known as CDAWeb which is under development in Code 630. The system presently provides access to both Key Parameter and high-time resolution datasets, and;
- Access to higher-time resolution data such as Geotail data from JHU/APL, University of Iowa and the University of Tokyo, Wind data from GSFC and GOES-7 data from NGDC University of Tokyo data are included for the above intervals and also for some additional time periods relating to the skimming campaign.
The event coordinator for the Skimming Campaign is Jim Green. If you have relevant data online and wish to make it available to the campaign participants, please send the relevant URLs to the coordinator at green@nssdca.gsfc.nasa.gov and they will be incorporated into the WWW pages.
In addition to the Skimming Campaign, the present WWW pages contain some information on the Event time periods selected by the Magnetotail and Substorm Physics working group. The coordinators for this study are Don Fairfield ( fairfield@lepvax.gsfc.nasa.gov) and Tusgunobu Nagai ( nagai@geo.titech.ac.jp). The WWW pages contain a general description of the objectives of the study and summaries of the observations made during some of the intervals which have been selected separately by the two coordinators. The time intervals are:
- Nov 22,23,24, 1994; Dec 1,2,3,4,10,11,12,13,23,24, 1994; Jan 9, 1995; Feb 18, 1995; Mar 9,13,14,25, 1995; April 26 1995. Selected by Don Fairfield.
- Oct 31, 1994 (various times); Nov 13,14,22, 1994; Various times on Dec 1,2,11,12,20,21,29,30, 1994; Various times on Jan 10,11,20,30,31, 1995. Selected by Tusgunobu Nagai.
Michael Teague and Jim Green
Goddard Space Flight Center
Code 630
Greenbelt, Md. 20771
teague@nssdca.gsfc.nasa.gov
green@nssdca.gsfc.nasa.gov
Key Parameter Availability
M. Acuna
Effective October 6, 1995, the National space Science Data Center (NSSDC) is authorized to publicly distribute Key Parameters from the following ISTP and associated investigations:
- All investigations on the WIND spacecraft: MFI, 3DP, SWE, WAVES, SMS, TGRS,EPACT
- The CPI and EPIC investigations from the GEOTAIL mission
- The MAG and PLA instruments on IMP-8
- DARN and SONDRESTROM ground-based investigations
- Geosynchronous orbit investigations from the GOES (MAG and EPS) and LANL (SPOA and MPA) spacecraft
Mario Acuna
Project Scientist
International Solar-Terrestrial Physics Program
Mailstop 695.0
Goddard Space Flight Center
Greenbelt, MD. 20771
u2mha@lepvax.gsfc.nasa.gov
KPGS PROGRAMMING FOR ALPHA AXP PLATFORMS
Gerry Blackwell
It is intended that KPGS programs running in the Central Data Handling Facility be capable of executing under open VMS on an ALPHA AXP computer, as well as the VAX. The CDHF will know which KPGS programs will not run on the ALPHA computer and will schedule them to run on the VAX.
The KPGS Integration Test Team has analyzed the existing production KPGS programs in order to determine what, if any, modifications are required in order for these programs to build and execute successfully on the ALPHA AXP computer. It was found that some minor modifications to these programs were required. Many require special compiler and linker options. At least one of the ICSS routines needed to be modified to replace a call to an assembly language routine with a call to a C language replacement routine. It was found that the compiler and the linker on the ALPHA AXP computer is somewhat less forgiving than that of the VAX. Therefore, the required modifications seem to be related more to programming practices than to programming errors.
To date, the following production KPGS programs will execute on the ALPHA AXP computer.
- GEOTAIL - EPIC, MGF,EFD,LEP,CPI
- WIND - MFI,SWE,EPACT,3DPA
- SOHO - COSTEP
The resulting key parameters generated on both the ALPHA and the VAX were identical.
As a result of our analysis of the current production KPGS programs now running on the ALPHA, we offer the following tips on programming practices to keep in mind when working on your KPGS program:
Tips for KPGS developers to ensure trouble-free ALPHA operation
- Use VAX system services only when absolutely necessary. Many of these services may not be available on the ALPHA computer.
- FORTRAN programs should not use Hollerith constants that span multiple source lines.
- Use the IMPLICIT NONE statement in all FORTRAN programs and subroutines to aid in detecting undefined and misspelled variables.
- Use the /WARNINGS=ALL compiler option when compiling FORTRAN modules, and /WARNINGS compiler option when compiling C programs to have all warnings and informational messages displayed. Some of these warnings may be fatal errors on the ALPHA.
- Use formatted files for calibration and instrument parameter files as much as possible.
- Do not use any assembler language code.
- Make sure there is a valid path to all source code statements. Be careful when deleting GO TO "label" statements because this may remove the only path to the "label" statement.
- Be sure to initialize all variables before they are used. Be especially careful with variables that are initialized in include files. The include file must be referenced in the subroutine.
Gerry Blackwell
Computer Sciences Corp.
7700 Hubble Drive
Lanham-Seabrook, Md. 20706
gblackwell@istp1.gsfc.nasa.gov
POLAR ORBIT AND ATTITUDE ISSUES
William H. Mish
This article discusses additions to the orbit, spacecraft and despun platform attitude, and spin phase files and modifications to the ICSS routines and IGRF model within the CDHF.
Introduction
Resident on the CDHF and on both the Level Zero and Key Parameter CD-ROMs are orbit, spacecraft attitude, despun platform attitude and spacecraft body spin phase (Level Zero CDs only) daily files which provide the spacecraft orbital position and attitude of the spacecraft body and despun platform at one minute resolution, as well as the spin phase of the spacecraft body. Orbit and spacecraft attitude are in GCI, GSE and GSM. These files are all encapsulated as Common Data Format (CDF) files.
I) Addition of EDMLT, Magnetic Latitude and "L" Shell:
Recently it has become apparent that the auroral physics being studied by the Polar spacecraft instruments would benefit by having available, as a function of the spacecraft position, the Magnetic Local Time (EDMLT), (which is magnetic longitude in units of hours), Magnetic Latitude (in units of degrees) and the associated "L" Shell parameter (in units of Re). These parameters will be computed using the eccentric dipole (ED) and IGRF January 1, 1995 magnetic model coefficients (no secular variations are included).
The above discussed parameters will be included in the Polar Orbit CDFs at the standard one minute time resolution of the orbital position and will be available to the Key Parameter Generation Software in the CDHF via a call to ICSS_COMPUTE_EDMLT.
II) Inclusion of a reference orbit number in the Polar orbit CDF:
The Polar Orbit CDFs will contain reference orbit numbers defined as follows:
An orbit is defined to start from the ascending node (when the Polar spacecraft orbit crosses the Earth's equator). The first fractional orbit before reaching the ascending node will be numbered zero and the subsequent orbits numbers will monotonically increase.
III) Additions to the despun platform attitude CDF:
At the Polar Despun Platform Meeting - 8/1/95 the PI teams with instruments of the despun platform requested that additional information be added to the despun platform CDF. (Note that the presently provided GCI, GSE and GSM pitch, roll and yaw is to be retained).
a) The despun platform attitude in GCI, GSE and GSM (this is the same coordinate system provided for the attitude of spacecraft body
b) The despun platform offset angle from Nadir
c) A despun platform in-lock flag
IV) Computation of a Sun Phase Reference Pulse during the spacecraft 180 degree turn-arounds:
We are looking into the feasibility of computing the Sun Phase Reference Pulse during these turn -around, the first of which, is in March 1996 (assuming a December 9, 1995 launch) and at 6 month intervals there-after, to be located in the spin phase CDF.
Table I below summarizes what these files will contain.
TABLE I
ORBIT CDF S/C ATTITUDE CDF DSP ATTITUDE CDF
S/C POSITION S/C BODY PITCH/ROLL/YAW
GCI GCI GCI
GSE GSE GSE
GSM GSM GSM
EDMLT BODY SPIN RATE DPA ACCURACY
INDICATOR
INV LAT S/C ATTITUDE ATTITUDE DSP IN
PRECISION METRIC S/C FRAME OF REF
DSP IN-LOCK FLAG
L SHELL NADIR OFFSET ANG
HELIOCENTRIC
S/C VELOCITY
GCI
GSE
GSM
HELIOCENTRIC
GCI SUN POSITION
CARRINGTON ROTATION #
ORBIT #
ORBITAL POSITION
PRECISION METRIC
V) Discussion of the orbit precision metric:
The orbit precision metric has been developed by constructing a difference vector between time -coincident ephemeris positions (e.g., time overlapping ephemeris positions computed from separate tracking data) that are to be compared and by measuring the components of this difference vector in a coordinate system fixed at the position of the spacecraft in the first ephemeris. Calling the coordinate system Sx, Sy, Sz, the Sx-axis is coincident with the geocenter radius vector to the spacecraft and is measured postive in the direction of the Earth's center. The Sy-axis is perpendicular to Sx in the plane and direction of the satellite motion. The Sz-axis is perpendicular to the plane of the motion and completes the right-handed system.
In the orbit CDF the "Radial", "along track", and "cross track" items are the Sx, Sy, and Sz components, respectively, of the difference vector. The "delta-r" and "delta-v" items are the magnitude of the difference vector for the position and velocity, respectively. Finally, the RMS is the standard deviation of the component differences over the length of the compared ephemeris. Thus the smaller this "error ellipsoid" the better the agreement between tracking observations.
VI) DSP Accuracy Indicator
This Indicator specifies whether the despun platform attitude is statistically good (=0) or bad (=1). The attitude is derived from a batch of computed attitudes at a fixed offset angle. Thus data are accumulated until either all the required data are collected or the offset angle is changed to a new value. A statistically good attitude from a batch is one in which no more than 1/9 of the original points were deleted during the least-squares fit process.
William H. Mish
ISTP Deputy Project Scientist for Data Systems
Goddard Space Flight Center
Mailstop 694.0
Greenbelt, Md. 20771
wmish@istp1.gsfc.nasa.gov
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